Indirect photomechanical reproduction



May 9, 1950 F. G. YANES 2,507,431 INDIRECT PHOTOMECHANICAL REPRODUCTION j Filed May 17, 1945 v FIGIO FIGS @HU mfi'mm mm mm .NVENTOR.

FIG ll Patented May 9, 1950 INDIRECT PHOTOMECHANICAL REPRODUCTION Francisco G. Yanes, New York, N. Y.; Anne F. Goddard executrix of said Francisco G. Yanes,

deceased Application May 17, 1945, Serial No. 594,287

6 Claims.

The invention relates to indirect photomechanical reproduction and includes means, ways, and products. It has to do in general with the production of relief surfaces, and specially of half-tone blocks and line-cuts. The system is indirect because the printing surface is firstly obtained in a reverse relief or mould from which a cast may be taken.

The present invention may be considered an improvement over my method of Indirect photomechanical reproduction described in Patent No. 2,374,910, issued May 1, 1945. It is, however, based upon another principle, and includes entirely new combinations and features which show novelty individually or in less combination than the whole as it will be later evidenced.

One of the purposes of the invention is to simpliiy the expensive installation and elaborate manipulations which are associated in the production of printing plates. Another purpose is to facilitate duplication by producing the mould at once, without firstly making an original plate. Other purposes concerning the quality of the reproduction will also be discussed in the examples of the present disclosure.

As it is well known two problems are involved in the production of relief surfaces. One of these problems is depth, which, in making line-cuts is a source of tiresome and multiple precautions in order to obtain a relief which still needs some complemental re-etching or mechanical routing. The other problem, in half-tone making, is the transformation of photographic values in depth into photomechanical values in surface. According to the present invention all this is solved in a simple way by two fundamental features which may be combined in some of the variations of the process.

The question of depth is met in the invention by producing a mould from a stratified material in which several thicknesses of matter are welded together that are soluble or etchable in different solvents. Depth is produced by successive etchings in alternate solvents without special precautions, as the material is self-protected; the appearance of every new stratum indicates when to change the solvent, each bite adding depth to the etching; and the bottom stratum or an insoluble base provides an even bottom for the mould. This combination in a mould offers other advantages, as permitting to obtain varied depths at different areas, and also the addition of supplemental matter at selected sections of its surface.

The transformation of the photographic values in depth into photomechanical values both in surface and in relief is attained in the invention by means of controlled etching. The action of etching is utilized, not only for discharging matter but for producing the values to be discharged. Etching, and in general, the discharge of matter may be and actually has been controlled in the invention as the effect of light in half-tone making. Etching may be screened through a resist, and may be proportioned to light values at given areas, and so it is capable of developing photomechanical values, with the advantage that they are already in relief. For the purpose of the invention two controls of the etching, at least, are utilized. One is a resist, which may be considered as the etching screen, for dividing the etching into a number of minute areas; the other control consists in the means for selectively proportioning the amount of the etching to a, given scale of values. These two controls may be used together for developing a halftone block. Or they may be used separately, by

' etching first under one of them, taking a cast in etchable matter, and etching again under the other control. This last technique is the one utilized in the present method for Indirect reproduction, by providing the worker with a developable moulding element in which the etching under the first control has been already performed and reversed, thus simplifying the operations. Developable moulds, otherwise produced, and similar to the etched one, are also provided by the invention which ofier some particular advantages. When building these other types of developable moulding elements, improvements in depth, texture, and other conditions may be introduced that will make them more adaptable to varied industrial applications.

For the purpose of demonstration, some examples showing the main features of the invention, both separately and combined, are presented in the following description.

In the drawings:

Fig. 1 diagrammatically shows in three stages the etching in depth of a shadow plate with flash dots of suitable size.

Fig. 2 is a cast or reverse structure of the final stage of Fig. 1.

Fig. 3 represents two sections of Fig. 2, after it has been coated with sensitive matter.

Fig. 4 illustrates two sections of Fig. 2, after it has been covered by a carbon tissue resist.

Fig. 5 is the mould resulting from the selective etching of Fig. 2.

Fig. 6 is a cast of Fig. 5.

Fig. '7 presents two examples of stratified material of varied solubility, one coated with sensitive matter.

Fig. 8 is a similar structure to Fig. 2, produced from Fig. '7, both with and without high-light casting cavities.

Fig. 9 is another structure similar to Fig. 2, produced by mechanical engraving, both with and without high-light casting cavities.

Fig. 10 is a combination of Fig. 7, and Fig. 9.

Fig. 11 is a diagram showing some exarnples of the variety of values and depths which be obtained through the invention. V

Fig. 1, shows in three stages the metamorphosis, of matter through the process of etching. In I, a shadow plate appears etched to the usual shallow relief; in 2, it has been etched "further, as to approach a half-tone surface; and in it has been etched in depth, until transformed into a high-light tint. It may be observed in three stages of Fig. 1, a sort of double ring, illustrating the way the etching proceeds, as in "spherical propagation, and by Segments of increasing area. "Etching is very similar to the effector light, the double rings rem'nding of the penu'mbra'l shadow suggested by Deville for ex plaining the efiect of the exposure upon a plate 'thro'ugh theengravingscreen. I have found etching maybe utilized not only for prodncing relief but for the developing of photoniechanical values. In the first stage I, of Fig. 1, the resist "on the shadow plate is the screen for the etching, and if I provide upon it means for proportioning the etching in depth to image-Values, the "structure '3, of the third stage of Fig. 1, will be a half-tone block. I have also found that etching is reversible, for I may use first only the resist'of the shadow plate, etching one way, then taking a cast and etching the other way under a negative carbon-tissue resist, and the result will be aniould for a half-tone block. The last system is the one utilized in the Indirect method of reproduction.

For demonstrating the reversion of the phenomerion I may take the cast in Fig. 2. There may be seen in it the small cavities l, which mould high-light dots; linking sections 5, which are partially'developedmoulding cavities for halftone values; andjtop areas'fi, whose difference of level with the b ottom'of the cavities' l, represents r the 'printingdepth of the high-lights in the cast, "a depth which can be controlled by adopting a suitable "si ze'for the flash dots in the first stage of Fig. 1,'for the smaller they are the deeper is the final plate. If we now take the structure of Fig. 2, and submit it to the same etching, it will be "foundthat the structure returns gradually, stage by stage-in casting values-'-to the initial shadow plate 1, of Fig.1. A

For demonstrating the production of a halitori'e block I may cover the structure of Fig. 2, with a carbon tissue resist bearing negative image-values of different permeability [9, it, which are shown in Fig. 4,'on two sections {and 8, of Fig. 2; then I'etch the plate, and the result is the mould in Fig. 5, where the section l, corresponding to'the high-lights appears unchanged, and that of the tones 811:, fully developed into casting values; and finally I take the cast ll, shown in Fig. 6, in which high-light dots lz and half to'ne values 13, are printable. Instead of a carbon resist, I may coat Fig. 2, with sensitive matter 9, as illustrated in Fig. 3, and produce thereon the image-values of varied permeability, or I may use any other was for creating a selective interference of the etching corresponding proportionally to image-values.

The most interesting fact in the above demonstration is the resulting texture of the printing pattern f or high-light and half -tones respectively. In my former patent on indirect reproduction, the etchable ground was the reverse shape of a high-light tint, formed by uniform, minute cavi ties decreasing in cross-sectional area and ending at the same plane. Through selective etching a mouldwas developed capable of casting 'dio'ts o'f different top areas furnishing photomechanical image-values, only that all of those values were represented in the print by black dots or different sizes on a white field until they appeared intersecting each other at the shadows. Now, ,the etchable ground illustrated in Fig. 2, furnishes the surprising result of the known dual patterh of photoengraving, namely black dots of different sizes in a white field for the high-lights, and small white areas, surrounded by an "encircling black texture for the half tone and shadows. Which is a further demonstration of the reversible phenomenon and the basic idea of the invention.

The gradually developed structure of Fig. 2, is illustrated as originated from ,9, regular shadow plate with flash dots of suitable "size, as produced through a photomechanical screen in known way. But, obviously, minute clear sections in an otherwise protected plate, regular or irregularly distrib'uted, will und'ergo the same "transformation through the process of etching. For example, a reversely grained plate, in manner 'familiar to engraver's, or any other fine and clear pattern produced in any other form.

I have also found that instead. of the gradually developed,'s'inglestructure of Fig. 2, several, or at least two "dilfer'ent patterns, may be combined in the same structure. It can be done in normal reliehfollowed by a cast. 01' the e'tchable ground'may be produced "atoms. The advantage in either case is that "the -artificially combined patterns are independent aridca-n be varied; and as separately developed, theyc'an be given not only the exact relativedepth but "any depth convenient to counteract the "flattening effect of the relief value *in some processes of the printing industry. But before discussing these other types of etchable grounds, and their "improved results, it seems necessary to'exainine the other fundamental feature of the invention.

The question of depth concerns both half-tone blocks and line-cuts. Indirectly it-has b'eendemonstra'ted 'alre ady that greatitlepth cannot simply be obtained by long etching because etching is a complex --phenom'enon-tending to 'a metamorphosis of the starting area. In order to attain depth by etching, several short and "independent etchings should be added. This'ha's been done in the prior art for normal reliefs by some elaborate operations purported to protect each of several successive bites. In the present invention and for producing a mould a s'tr'atified material is utilized combining plural thicknesses of difierent substances soluble indifferent solvents. A the solvents can be easily changed the result of'each bite needs not'any protection. The'time and-labor which can befsaved wouldb'esufiic'ient to justify this feature'of the invention if there were 'not other'most useful new results in suchcor'nbin'ation.

In Fig. 7, two examples "of stratified material are shown in which plural thicknesses of matter 75 appear welded that "are soluble in difier'ent solvents. In the first of these examples the combination includes a thickness M, a narrower thickness l5, and the insoluble base l6. Such specific arrangement has been devised for purposes to be later explained and by no means should be considered as limiting other possible variations. In the second example a greater number of thicknesses are supported by the insoluble base it, and covered by a sensitive layer I]. or these thicknesses those of a group [8, are soluble in a solvent different than the solvent of the group I9.

Thesecond example in Fig. 7, is purported for obtaining depth and suitable for making linecuts, or rather moulds for line-cuts in the indirect system of reproduction. The element has been illustrated as coated with sensitive matter but the bare material is the new and essential member of this combination, for even the insoluble base may be replaced by a protective coating. It may be noticed that the strata are all thin and that those of one group are interleaved among those of the other group. The thickness of every foil or stratum and the number of them, will depend upon the etching depth to be obtained. In the arrangement, instead of several substances soluble in different solvents, only two substances have been utilized in alternate position as equally efiicient for the mere purpose of securing depth by etching. For the rest the material may be used as ordinary sheet metal until the selective protection is produced on the top stratum. The etching is started in one of the solvents and, when the second stratum is visible, the element is transferred to the second solvent and so on. The strata which have been already etched will again be attacked by the solvent in every change, and the etching will enlarge the cavities progressively from the bottom to the outer surface, but the important point is that, when a thickness begins to etch, the immediate stratum covering it will not etch, and the demarcation of the etchable area will be neat. The insoluble support or any stratum at which the etching stops will furnish an even bottom for the cast. Instead of two, sets of three or more substances and their corresponding solvents may be utilized. When all the strata and solvents are different the etching will be straight to the bottom and the cavities will not decrease in cross-sectional area as when several alternate strata or sets of substances are utilized. Once the etching is finished, additional thicknesses of matter may be added to the surface of the mould before casting, thus making unnecessary the routing of the final relief surface.

The idea of dissolving a substance under the protection of another is not new in general, for in most etching processes such step is fundamental; it is not even new to dissolve selectively under the sensitive coating the real protection or resist under which the etching will be performed, as in some enamel variations, and particularly for the etching of steel with iodine, in which a copper thickness is firstetched with ferric chloride that will act as resist for the protection of the steel. But the specific idea of the invention is to etch in such manner not one but several thin layers, each of which acting as resist for the next one, after adding certain depth to the etching, under the knowledge that depth cannot be suitably developed by long etching of a single substance without elaborate precautions. According to the invention thin layers of a single substance may be Welded provided a separating coating or binder soluble in another solvent is interposed among the strata. When substances susceptible of being hardened are utilized, the element may be placed for a few seconds in a hardening bath before passing it to the next solvent. Another differentiation with the prior art is that the stratified material in the present invention is not purported for producing regular printing depth but moulding depth. If a normal relief were directly produced in a stratified material the resulting product would also be stratified and necessarily weak, as formed by several layers of different substances which may break or separate under the effect of dilatation or the pressure used in relief printing. In the Indirect system the mould is stratified but the cast is not, and the finest lines of the design will be formed by a single substance which does not present the weakness of a stratified structure. The combination suggested in the present invention thus provides both depth and strength. On the other hand, the substances exclusively soluble each in one solvent are rather limited, considering the number required for obtaining great depth, and quite elaborate to have so many etching baths. According to the invention several sets of foils of different sub stances, even two, may be alternated and repeated in the etchable material, as illustrated in the second example of Fig. 7. This can be done precisely because the stratified material is purported for a mould, and the re-etching of formerly etched foils merely widens the outer sections of the mouldin cavities. But when a n0rmal relief is produced it is notsuitable to use repeated sets of substances in a stratified material, because when foils already etched are etched again the relief values are undercut and become weaker still. In the case of a mould the widening of the upper sections of the cavities is rather favorable, as it provides in the cast a stronger base for relief values of great depth. The Indirect system for producing line cuts further presents the exclusive advantage of permitting the addition of supplemental thicknesses for still greater depth at sections of the mould corresponding to large white areas. The combination, however, is not only useful for attaining moulding depth, but has some other interesting possibilities.

Let us assume that instead of the gradually developed single structure illustrated in Fig. 2, we wish to produce a combination of two independent patterns, as for instance, a relief texture of crossed lines having protruding dots at the crossing points of the lines, which includes the connected graphic elements for the halftones and the isolated graphic elements of minimum area for the high-lights. And let us assume further that we require a ruling of 64 lines, a ratio of 3:1, and a total depth greater than known average amounting to 0.010 of one inch, of which 0.006 will correspond to the connected elements and 0.004 to the isolated minimum dots. For this we may first disassemble the two halves of a photomechanical screen in order to obtain a screen of parallel lines which we print on process film in the camera until a copy with the 3:1 ratio is provided. Then we produce the structure of the first example of Fig. 7, by taking a thickness of copper of 0.006, another thickness of aluminum of 0.004, and a thickness of insoluble base, and weld them together. And finally, after havin the screen and the etchable material we proceed as follows: 1. A resist of parallel lines is produced on the copper thickness which is etched in hydrated ferric chloride until the aluminum is visible and the resist is removed. 2. A second resist of parallel lines is produced on the copper perpendicularly to the first set of lines. 3. The plate is etched in hydrochloric acid which will not attack the resist or the copper lines but the bare aluminum dots down to the insoluble support. 4. The plate is etched again in hydrated ferric chloride until the crossed lines are visible on the aluminum thickness. And a structure is finished which can "be used or duplicated, as the one illustrated in the first example of Fig. 8, where high-light cavities 4x, linking half-tone cavities 5a, of lesser depth, and raised sections 60:, may be seen which are equivalent to similar casting values in Fig. 2. When a relief pattern is desired without highlight casting dots, for producing a half-tone block with pure whites, the etching of the aluminum thickness is omitted and the structure Wil have the appearance of the second example of Fig. 8. The advantage of combining two independent patterns consists in the complete control of the requirements for the structure. The possibilities of the stratified material of Fig. '7, are thus further evidenced.

I may also produce a similar dual patterned structure by mechanical engraving, as illustrated in Fig. 9. For this purpose I first cut parallel grooves in two perpendicular directions on a brass plate, then I take a cast, and add raising dots at the crossing points ofthe walls, or equivalently reduce the height of the walls mechanically or by a technique similar to reetching. And finally I take a second cast illustrated in the first example of Fig. 9, in which highlight cavities 4c, linking casting cavities of lesser depth 52, and raised sections 62, are shown which are equivalent to similar casting values in Fig. 2. When no high-light cavities are desired I simply cut the two sets of perpendicular crossed grooves as shown in the second example of Fig. 9. It may be noticed that in the last two examples the cavities decrease in cross-sectional area towards the bottom which is favorable to speed up the etching.

The structures of Fig. 2, Fig. 8, 'Fig. 9, and other similar ones, may be further combined with the stratified material of Fig. '7. An example of this combination between Figs. 9, and 7, is illustrated in Fig. 10, in two sections similar to the sections of Fig. 2, seen in Fig. 3. The first section is, of Fig. 10, shows high-light, and the second section 32, half-tone cavities of lesser depth. It is easy to realize "that when this combination is covered by a resist, as H], in Fig. 4, the high-ligh cavities are not etched and when the halftcne cavities reach the thickness l5. Fig. 10, a second etching with a second solvent will make them deeper than the high-lights and so the half-tone printing values will correspondingly be raised in the cast.

By suitably using or combining the two fundamental features of the invention a variety of values and depths may be obtained of which some examples are diagrammatically shown in Fig. 11. When producing any of the'dual patterned structures in a single thickness of matter the depth of the etched cavities, as corresponding to photographic values, will increase gradually from high-lights to shadows and the cast will show a bump proportional to the photomechanical values as in the first example of Fig. 11. If only a half-tone pattern is utilized in-the single thickness a gradual bump. will also be obtained in the cast without high-light dots,

as in the second example. The use of a stratified material and a dual pattern will give in a single etching high-lights, half-tones and shadows of the same height, as in the third example, while two etchings with two solvents will raise half-tone and shadows to the same level and above the high-lights, as in the fourth example of the figure. Finally, a half-tone pattern in a stratum of suitable thickness in the same material and two etchings will give values of the same height and unprintable pure whites. Etc.

For understanding the useful purpose of the invention it may be convenient to observe that the developable grounds illustrated in Figs. 2, 8, and 9, are not supposed to be manufactured by the worker; they are master plates from which inexpensive duplicates can be produced and -offer-ed to the public. Those grounds constitute partially made moulds, having already some minimum values and which only need to :be completed. Hence the simplicity of the process, because the etching :under the preferred control of a gelatine image does not required any special installation or particular skill. Whether the ground be covered by a sensitive coating in which the selective permeability is created, or whether a carbontissue resist is transferred and developed on the unfinished mould, it is the etching that performs the transformation of the photographic values in the gel'atine image into the photomechanical casting values of the mould. So, while the etching progresses, it is possible to follow the formation of the casting values as a developing operation. And indeed an ideal one, because the etching technique through gelatine resists permits to act selectively upon different tones by using etching solutions of varied concentration. The etching of :the ground is the same practiced in photogravure and so well'known in the literature that it seems prolix to enter into details. It was, however, summarized in my former patent on the indirect system .of reproduction.

There are, of course, many other ways of producing .a selective protection on the developa'ble moulding element, even by hand as .anartist may at once produce a design already in photomechanicalvalues; and there are also many other ways of producing the discharge, even mechanically, which are the scope of the invention, but we have given preference in :the examples to those which require the minimum installation and work, "both for simplicity and economy.

The .developable ground when made of a single substance, etched, and cast, furnishes a product which seemingly is new to the art, because the photomechanical values have agradual differ ence of height in correspondence with their printing area. It is well known that for some printing operations a.raise.ofbump of the tone values is conveniently made in the printing blocks, here it is automatically obtained with the advantage that it is proportional to the values and preserves the gradation of the'tones. When, for some other'kind of printingit is desired that the Values be all produced at the same plane or part in one plane and part-in another, the invention provides means for limiting :the depth of the etching, so that the values which attain that depth bestopped while the other -values are developed. It 'further provides, by a combination of substances and solvcnts a. mannerof: obtaining -arselective depth. The niroumstancezthat.

theshigh-light.sections.are-protectedby themsetive values of the resist allows a further etching of the tone values.

A provision which has been considered unnecessary to illustrate concerns a precaution which may be convenient when developing moulds of coarse rulings requiring a longer etching. In that case it is prudent to provide a surface protection at the sections corresponding to the bottom of the cast which in the mould appear at the outer plane. These sections are illustrated in 6, 6:0, and 6a, in Figs. 2, 8, and 9. The purpose of that precaution is to preserve those sections as supporting areas for the resist.

Another provision which does not require illustration, but should be mentioned in a complete disclosure, concerns the transfer of the resist on the etchable ground. In my former patent the ground was provided with individual minute cavities which by a suction developed during the drying produced the strong and perfect adherence of the resist. In the present invention the ground does not present the same shape, and the adherence of the carbon-tissue may be facilitated by painting and drying on the ground before the transferring a marginal edge of gelatine. This precaution is, of course, unnecessary when using a sensitive element, as should be the case for making part plates in order to preserve the exact dimensions of the images.

There is another aspect of the indirect method which has been given special consideration in my former patent and which equally concerns the present invention. The ground itself may be sensitive to light, the demarcation of the etchable zones selectively made by the exposure, and these dissolved in known way. Such material will be similar to the one illustrated in Fig. 10. This variation would not be practicable in all types of grounds because the efiect of light is straight and not in all directions as that of etching. But for a ground in which the relief sections decrease in cross-sectional area, or in combination with other ways for developing the values in surface. the variation is practicable. The resulting mould, however, would present casting limitations which are not found in the one produced by selectively discharging matter from a ground which is not sensitive to light.

The ground illustrated in Fig. 2, in its normal shape of 3, Fig. 1, is equally developable into a half-tone block by other processes which, instead of discharging, will add matter proportionally to the values to be reproduced. As the relief sections of 3, Fig. 1, decrease in cross-sectional area, the element can be produced in a transparent substance and utilized in the Direct method of reproduction, as described in Patent No. 2,234,997, issued March 18, 1941, and in my pending application Serial No. 591,673, dated May 3, 1945, now abandoned. The same applies to normal structures cast from a ground as the one illustrated in Fig. 9, in which the relief sections decrease in cross-sectional area. For types of patterns lacking this requirement, as those of Fig. 8, the addition of complemental matter may be produced according to the method described in my pending application Serial No. 531,566, dated April 18, 1944 now issued as Patent 2,441,609. The present invention utilizes the reverse shape of all those and similar structures susceptible of being developed into a mould for a printing surface.

The varied products of the invention may be identified in the cast by a. residual undeveloped pattern present in the inner sections of the relief surface. The high-lights, for instance, from which there is not any discharge of matter will show linking minute reliefs between the dots; and in casts from grounds lacking high-light pro- -jections, some sections will show a printable pattern of connected graphic elements on the top and a second and unprintable bottom pattern of undeveloped similar values. These products may be further differentiated from those of Direct reproduction in that the relief surface is now made of a body of solid and continuous material and not by a fundamental pattern of one substance and additional complemental values of another substance. As to the products of .my

greatly favors the scale of tones in the reproduction.

After having disclosed to the best of my knowledge what I consider my achievement, I wish it to be understood that the examples presented are meant for demonstration only and do not limit the invention which may be susceptible of equivalent changes and variations within the scope of the following claims.

I claim:

l. The method for producing indirectly a halftone block which consists in first, providing an etchable shadow plate having an etching protection on its surface except in small clear sections; second, etching said plate in depth until the small clear sections become so enlarged that the unetched areas at the surface appear as minute high-light dots; third, taking a cast of the etched plate in etchable matter, in order to transform the relief values into the casting values of a mould; fourth, etching the mould after previously providing means capable of proportioning to positive image-values the etching action on its surface; fifth, carrying the etching of the mould until the casting values for the shadows have attained the appearance of the original shadow plate; sixth, cleaning the mould; and seventh, taking a cast from the etched mould.

2. The method of making a ground susceptible of being developed by selective discharge of matter into a mould for a half-tone block which consists in first, Welding together three continuous thicknesses of matter of which the upper one is soluble in a first solvent, the middle one in a second solvent, and the bottom one insoluble; second, producing on the upper thickness a resist showing half of a texture of connected graphic elements in one direction and etching with the first solvent; third, cleaning off the first resist and producing another resist of the second half of the texture in crossed direction to the first one; fourth, etching with the second solvent; and fifth, etching with the first solvent.

3. The method for producing a half-tone block for typographic printing which consists in first providing a ground having casting values for high-light dots and also minimum casting values of lesser depth for a tone texture; then discharging matter from said ground under controlling means proportioning the discharge to the values to be produced; and finally taking a cast from the resulting mould.

4. The method of producing a half-tone block with pure whites as those utilized in photolithog raphy which consists in first, producing in the top stratum of a stratified material formed by different substances soluble in difierent solvents a hollow pattern casting a minimum half-tone printing texture; second, discharging matter from said ground proportionally to the values to be reproduced; fourth, further discharging matter from the areas corresponding to the halftones and shadows until reaching a stratum whose depth is such in relation to that of the unaltered sections corresponding to the whites that the pattern corresponding to those sections in the cast will be unprintable; and fifth, taking a cast from the developed mould.

,5. In a mould for a half-tone block, plural strata of different matter welded together and showing high-light casting cavities ending atone of the strata and second casting cavities for halftone and shadow values represented by connected graphic elements ending at a lower stratum.

6. The method of producing a half-tone block for typographic printing, which comprises first providing a moulding element of etchable matter haying selectively distributed partially formed casting values corresponding to relatively different printing values of a half-tone texture, then selectively etching said element and discharging matter therefrom in proportion to the printing values to be produced, and then finally taking a cast from said element to form the printing surface of a half-tone block. h

F. G. YANES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 522,567 Winkel July 3, 1894 758,599 Sachers Apr. 26, 1904 1,166,540 Orans. Jan. 4, 1916 1,681,447 Torrison Aug. '21, 1928 1,849,036 Ernst Mar. 8, 1932 1,887,872 Ernst Nov. 15,, 1932 1,912,482 Huebner June 6, 19.33 1,991,888 Ernst Feb. 19,1935

2,091,715 Murray Aug. 30,, 1937 2,315,903 .Ormond Apr. 6, 1943 2,316,595 Hartmut Apr. 13, 1943 2,322,530 MacArthur June 22, 1943 2,374,910 Yanes May 1, 1945 OTHER REFERENCES Commercial Engraving and Printing, Hackleman, published by Commercial Engraving Publishing Co. (1921), Indianapolis, Ind., page 245. (Copy in Division 17.) 

